InPHBTDigital ICsandMMICsinthe140-220 GHzband

Well-balanced InPHlBTsnow have-450GHz cutoff frequencies and-4Vbreakdown. Withsuchdevices, 150GHz digital circuits (static dividers) and175GHzamplifiers have beendemonstrated. We discuss device requirements (scaling lawsandscaling limits) forrealizing transistors andboth digital andanalog/RF circuits atsub-mm-wave frequencies; the mostcritical limitations aremetal/semiconductor contact resistivities anddissipated powerdensities. Givenpresent contact performance andthermal design, 200GHzdigital technologies and300GHzpoweramplifiers arenowfeasible andwill soonberealized. Sub-mm-Wave Transistors: Present & Future Radios, imaging systems, andradars today employ transistor circuits onlyatlowmm-wavefrequencies, withhigher frequencies served by Schottky diodes, vacuumelectron devices, andgaslasers. Travelling-wave vacuumdevices offer muchhigher output powerthan transistors, lasers offer amuch wider frequency range, andbothlasers andbolometers offer lower noise. Despite these disadvantages, transistors offer key attributes which motivate ustoextend their operation tosubmm-wavefrequencies. Transistors areverysmall, areefficient poweramplifiers, andcanbevery reliable. Unlike diodes, THz tubes andlasers, transistors serve manyfunctions, including amplifiers, oscillators, mixers, harmonic multipliers, switches, andlogic gates. Withtransistors, onecancompactly construct a wealth ofimportant communications circuits, including PLLs andfrequency synthesizers, monolithic frequency multiplier chains, QAM (de)modulators, superheterodyne receivers, and monolithic phased arrays.